How To Proceed With Troubleshooting
WARNING: This page is about a different car, the 2004 Lexus GS 430 and 2004 Lexus GS 300. However, it is still accessible from the selected car via links, so may be relevant.
HINT:
The ECU of this system is connected to the multiplex communication system. Therefore, before starting troubleshooting, make sure to check that there is no trouble in the multiplex communication system.